1. Field of the Invention
The present invention relates to a toner supplying roller in a developing apparatus in an image forming apparatus employing an electrophotographic printing method or an electrostatic recording method, a developing apparatus, and an image forming apparatus.
2. Description of the Related Art
In an image forming apparatus such as an electrostatic copying machine and a printer, a latent image on a photosensitive member is developed into a developer image by toner that is a developer from a developing roller of a developing unit and visualized. In this case, in the developing unit, toner conveyed with being agitated is supplied onto the developing roller by a supplying roller. Then, the toner is conveyed to a developing portion where the photosensitive member and the developing roller are opposed to each other, with a thickness of a toner layer being adjusted by a toner regulating member (hereinafter, referred to as a developing blade) on the developing roller.
Recently, the above-mentioned image forming apparatus is required to perform higher speed printing and suppress power consumption. Accordingly, toner with a low viscoelasticity, which can be fixed with a small amount of heat, is selected to be used in many cases.
In contrast, the toner supplying roller is required to supply the toner onto the developing roller, scrape off unnecessary toner, and supply the toner uniformly to the developing roller. In order to satisfy those two functions, a roller with satisfactory open cells formed at the surface thereof has been developed.
However, in a laser beam printer (LBP) using toner of a low viscoelasticity, the state of the toner may change (e.g., flowability of toner may decrease) depending upon the use conditions thereof or the number of sheets to be used, as the use of the developing apparatus progresses. In this case, a toner inhaling amount by the toner supplying roller and an exhaling amount to the developing roller may change.
In such a case, in a developing apparatus using the above-mentioned toner supplying roller, the supply amount of the toner changes depending upon a ratio of the total area of foam cell opening portions to the surface area of the toner supplying roller (hereinafter, referred to as opening ratio). When the opening ratio is large, the image defects may be caused by an excess supply of the toner to the developing roller when the developing apparatus is new. When the opening ratio is small, the image defects may be caused due to shortage of the toner supply as the use of the developing apparatus progresses. Therefore, it becomes very difficult to appropriately set the opening ratio of the toner supplying roller.